The report lays bare the dollars needed for Liberals to meet 2015 promise.

Canadian Press

John Woods/CP

A boy from the Shoal Lake 40 First Nation sits on a bridge over a channel on June 25, 2015.

OTTAWA — The parliamentary budget officer estimates it will cost at least $3.2 billion in capital investment to bring First Nations water systems up to the standards of comparable non-Indigenous communities in order to eliminate boil-water advisories by 2020.

The spending watchdog's latest report estimates the cost of updating drinking water systems at $1.8 billion, with another $1.4 billion needed for wastewater treatment and annual operating and maintenance costs of $361 million — $218 million of which would be for drinking water alone.

The report lays bare the likely dollar figures necessary for the Liberal government to make good on its 2015 campaign promise to eliminate boil-water advisories on reserves within five years.

Grits spending 70 per cent of what's needed

So far, the number of long-term advisories on systems supported by Indigenous Affairs had dropped by just seven — from 77 to 70 — as of the end of July.

The PBO says the total spending by the federal government and others since 2011-12, combined with spending measures announced in the 2016 budget, can only cover 70 per cent of the total investment necessary.

The report cautions that its estimates are sensitive to assumptions about population growth and other demographic factors, as well as a variety of capital investment options.